A mathematical model of a high sulphate wastewater anaerobic treatment system

As an aid to the design and operation of anaerobic digesters treating high sulphate waste waters, a mathematical model describing this treatment process has been developed. Apart from sulphate reduction, the model includes those reactions which occur either prior to sulphate reduction or in competition with it. These include, hydrolysis of solid substrates, acidogenesis, beta oxidation of long chain fatty acids, acetogenesis and methanogenesis. By incorporating terms for these reactions the model is able to simulate sulphate reduction using a wide range of carbon sources. Acid/base equilibrium chemistry is included in order to predict the pH and unionized component concentrations, needed for calculating inhibition. An activity based model is used, with the activity coefficients calculated using Debye–Hückle theory. The mass transfer rates of hydrogen, methane, carbon dioxide and hydrogen sulphide from the liquid to the vapour phase are also included. A number of different reactor types may be simulated, including a dynamic batch, steady state CSTR and dynamic CSTR. By separating the hydraulic and solids residence times, high rate reactors such as UASB and packed bed reactors may also be simulated. The model has been used to successfully predict the dynamic and steady state behaviour of a number of different reactor types, utilizing both simple and complex carbon sources.